It's possible that an SBxBCM cross could lay a brown egg, but I'd expect primarily some shade of olive. The OP, @gapey, wrote this post on her blog that I think may be helpful.I have a egg color genetics question for all of you about SBs. Do they carry 2 blue egg genes (OO)? I’m trying to figure out if all the F1 chicks from a SB x Marans cross will lay olive or if some will just lay brown. I don’t totally get how the green egg genetics work since it’s so unusual. I have my mind wrapped around blue, brown and white but the pieces aren’t clicking in my brain about how the SBs breed true for green eggs.